1. Field of the Invention
The invention pertains to farm machinery and, more particularly, to means for detecting the clearance between two proximal ferrous elements in relative motion.
2. Description of the Prior Art
In some machines, the clearance between certain elements in relative motion may greatly affect the operation and efficiency of the machine. For example, in farm machinery, such as a forage harvester, the clearance between the cutter head knives and its associated shear bar may substantially affect the amount of fuel used in the operation thereof and also affect the food quality of the forage therefrom. A forage harvester is a farm machine that picks up crop or forage from the field and chops it into small pieces to enhance the food quality and the storage characteristics thereof. The chopping action takes place in the machine by means of a cutter head, having a plurality of knives mounted on its external perimeter rotating past a fixed shear bar, between which the crop or forage is conveyed. Thus, the clearance between the knives and the shear bar will readily affect the type of cut of the forage, for example, if the clearance between the knives and the shear bar is too large, a bad cut of the crop will occur reducing the food quality of the forage and increasing significantly the energy required. Accordingly, a minimum clearance, preferably as near zero as practical, is preferred. However, due to the fact that both the cutter knives and shear bar wear with use and with sharpening of the knives variations of the clearance of several thousandths of an inch are possible from knife to knife and from one end to the other end of any particular knife. It is apparent, that during operation the clearance of the knives may substantially increase, affecting the operation at its most inopportune time. In order to correct the situation, the operator must stop the operation of the machine, open the housing enclosing the cutter head and shear bar and if desired and practical, the operator may manually measure the clearance, for example, by means of a feeler gauge. This procedure is not only tedious and time consuming, but also inefficient and potentially dangerous. Furthermore, many forage harvesters do not provide easy access for manual measurement with a feeler gauge and, therefore, because of the time required for this procedure, fine tune adjustments of the clearance between the knives and the shear bar are neglected and an average clearance is generally provided for. Such an average clearance is, naturally, far from the optimum.
Accordingly, there is a need to provide efficient and rapid means for determining the clearance between elements in relative motion without requiring manual access thereto and shutdown of the machine and which may be utilized during the actual intended operation of the elements.